Electrochemical and Thermodynamic Properties of UCl3 in LiCl-KCl Eutectic Salt System and LiCl-KCl-GdCl3 System

The electrochemical techniques including cyclic voltammetry (CV), open circuit potential (OCP), and electrochemical impedance spectroscopy (EIS) were performed to understand fundamental behaviors of UCl3 in LiCl-KCl salt at concentrations ranging from 0.5 wt% to 4 wt% and temperatures from 723 K to 798 K. In addition, the same measurements were performed in LiCl-KCl-UCl3-GdCl3 for evaluating the effects of GdCl3 co-existence on uranium properties. Diffusion coefficients (D) of UCl3 was calculated by measuring reduction peaks of U3+/U in CV experiments. The values of D were linearly correlated with temperature, but weakly affected by concentration under 4 wt% of UCl3. The addition of GdCl3 showed no significant changes in D values. The equilibrium potentials (E) of U3+/U couple were measured from OCP data and no significant influence of GdCl3 was observed on the E trend. From the measured E values, the apparent standard potentials and thermodynamic properties of U3+/U were calculated and reported in this study. Lastly, EIS measurements were performed to explore the exchange current densities (i(0)) of U3+/U, showing linear relationships with both temperature and concentration, which were expressed using a simple linear correlation. Values of i(0) followed the same linear expression regardless of GdCl3 presence in the system. (C) 2017 The Electrochemical Society. All rights reserved.